[infra] Trigger CQ builders on changes to their individual directories.

This will ensure that when the properties file for a builder that is on
the CQ changes, the builder will be run with the new properties values.
In the future when test specs and GN args are specified in starlark,
they will similarly benefit from triggering the affected CQ builders.

Bug: 1378753
Change-Id: Ida58bbe4ec6bca6bc232e13f6997e17959c8df63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3984805
Commit-Queue: Garrett Beaty <gbeaty@google.com>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1064941}